1. Field of the Invention
The present invention relates to a ball bearing having a crown-shaped retainer made of synthetic resin, and more particularly to a ball bearing with a crown-shaped synthetic resin retainer (hereinafter, retainer) for supporting a spindle used for a device necessary for spinning, such as a spindle motor of a hard disc drive (HDD in general).
2. Background Information
Generally, a ball bearing has an annular configuration and comprises an inner race, an outer race, a plurality of balls fitted between the inner and outer races, and a retainer arranged between the inner and outer races and having a plurality of pockets for retaining the balls. The retainer comprises an annulus, pockets formed on one of the annular surfaces of the annulus, and a plurality of fingers or pawls formed at opposite sides of the pockets and axially projecting beyond the annular surface so as to prevent dropping out of the balls.
FIG. 6 is a cross-sectional view illustrating a conventional ball bearing as applied to, e.g., a HDD spindle. In the drawing, the ball bearing is partly enlarged for the purpose of indicating elements relating to the present invention.
Reference numerals 61, 62, 63, and 64 denote an inner race, an outer race, a ball, and a retainer, respectively in a ball bearing device. Furthermore, reference numeral 65 denotes an annulus which is of a flat surface. In the retainer 64, one of the annular surfaces 65a has a plurality of pockets 66. Each of the pockets 66 has a pair of pawls formed at opposite sides and project axially beyond the annular surface of the retainer 64. The pair of pawls 67 serve to prevent the dropping down of the respective balls 63. It will be understood that the annular surface 65a is formed in the shape of a flat surface between the pawls 67, whose surface is perpendicular to the axis. The pockets 66 are part-spherical or troidal-shaped such that each ball 63 is retained by a respective one of the pockets 66. The flat surface 65a serves to provide a predetermined amount of grease 68 so that the ball bearing is lubricated.
When the conventional retainer as above described was applied to a spindle motor for HDD, large quantities of grease 68 were scattered as the rotation of the ball bearing was increased. The scattered grease 68 was supplied to excess, because the released grease 68 was scattered toward the outer race 62 by the centrifugal force. As a result, this caused problems of increases in the resistance to agitation of grease and running torque. FIG. 7 is a cross sectional view showing a retainer for a ball bearing having an improved construction as compared to the retainer shown in FIG. 6. Such retainer is disclosed in Japanese Unexamined Utility Model Publication No. 2-85013. In the retainer for the ball bearing, there are provided protrusions 69 formed on the annular surface 65a of the annulus 65 between the rear faces of the pawls 67, respectively. The retainer 64 also has areas which are greased.
In the conventional retainer shown in FIG. 7, pawls 67 cannot effectively prevent the grease 68 from being scattered toward the outer race 62. However, it is difficult to set or coordinate an amount of grease to be supplied to the outer race 62. That is, if the grease is supplied to the outer race 62 in less quantities than required, the ball bearing will shorten its life because the outer race is not lubricated with grease.
In order to solve the above problems, the present invention is to provide, a ball bearing having an inner race, an outer race, a plurality of balls fitted between the inner and outer races at spaced equally intervals, and a retainer comprised of an annular member, a plurality of pockets formed by recessed openings on a first annular surface of the annular member, and a pair of fingers or pawls formed at opposite ends of the pockets and axially projecting beyond the first annular surface of the annular member. The first annular surface of the annular member has a surface portion formed in a slant which is inclined toward a second annular surface of the annular member from the external edge to the internal edge of the former.
In addition, the present invention is to provide an improved retainer by forming pawls which are of a thick wall along an outer curved line of the annular member and which are of a thin wall along an inner curved line of the annular member so that a space is tapered from the internal edge to the external edge of the annular surface between the back faces of the pawls.
According to the present invention, recesses for inserting a projected pin, which is utilized to stamp out or release the molded retainer from the die, enables a supply of a lubricant from the inner race to the outer race to be controlled.